System and method for purifying depleted brine

ABSTRACT

A system and method for removing impurities to reconstitute a NaCl stream to a saturated solution salt solution and remove any impurities such as sodium bisulfate (NaHSO3), sodium chlorate (NaClO3) and sodium iodide (NaI) to improve brine quality from an electrolytic cell is disclosed, including an evaporation system connected to the electrolytic cell, a brine treatment system connected to the evaporation system and the electrolytic cell. A waste treatment system is connected to the evaporation system. The evaporation system includes a set of evaporators that concentrates the brine. Sodium chloride is precipitated from the set of evaporators to the brine treatment system. Impurities are precipitated from the set of evaporators. The brine treatment system includes a hydrocyclone and a centrifuge that separates sodium chloride from water. The sodium chloride is mixed with water to create a concentrated and purified brine.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/088,152, filed Dec. 5, 2014. The patent application identified aboveis incorporated herein by reference in its entirety to providecontinuity of disclosure.

FIELD OF THE INVENTION

The present invention relates to the treatment of waste streams. Inparticular, the present invention relates to treating depleted brinefrom a chlor-alkali processing system.

BACKGROUND OF THE INVENTION

Chlor-alkali systems and processes produce chlorine, sodium hydroxide(caustic soda) and other caustic alkali products. Typically, the processis conducted in an electrolytic membrane cell using a brine, which is anaqueous solution of sodium chloride. The brine is fed into theelectrolytic cell, which includes an anode side and a cathode sideseparated by a membrane. A current is passed through the electrolyticcell. As a result, the sodium chloride brine splits into its constituentparts. The membrane allows sodium ions to pass through it to the cathodeside, where it forms sodium hydroxide in a solution. The membrane allowsonly positive sodium ions to pass through to prevent the chlorine frommixing with the sodium hydroxide. The chloride ions are oxidized tochlorine gas at the anode. Hydrogen gas and hydroxide ions are formed atthe cathode. After this process, the brine is depleted and cannot beused in the electrolytic cell. Therefore, the depleted brine must betreated or replaced with fresh brine in order for the membraneelectrolytic cell to properly operate. Further, the depleted brine mustbe purified to remove impurities that may cause fouling of the membrane.

The prior art has attempted to address the need for purified brine withlimited success. For example, U.S. Pat. No. 4,169,773 to Lai, et al.discloses a system and method for the electrolytic production of alkalimetal hydroxide and halide with acidification of part of a recirculatinganolyte stream to remove halite. The system in Lai diverts a brinestream from a membrane cell to a reaction vessel for treatment. In thereaction vessel, concentrated hydrochloric acid (HCl) is added to thebrine stream to minimize chlorine dioxide production. The treated streamis then irradiated with ultra violet light. The irradiated stream ispassed through a scrubber before being reintroduced to the membranecell. However, the system in Lai requires the use of hydrochloric acidand an irradiation step that increases costs and inefficiencies.

U.S. Pat. No. 6,309,530 to Rutherford, et al. discloses a system andmethod for the concentration of depleted brine exiting a chlor-alkalimembrane cell plant. The depleted brine flows from a membrane cell intoa dechlorinator where chemicals, such as sodium carbonate and sodiumhydroxide are added. The dechlorinated brine is fed into a concentratorsystem where water vapor is removed. The reconcentrated brine is thenready for use. However, like Lai, the system in Rutherford requires theaddition of chemicals, thereby leading increased costs.

Therefore, there is a need in art for a system and method for purifyingbrine that does not add chemicals to the brine and does not requirecostly compression and/or condensation steps. Thus, there is a need fora system and method of purifying depleted brine with minimal costs andsteps to treat the depleted brine.

SUMMARY

In a preferred embodiment, a system and method for concentrating andpurifying depleted brine from an electrolytic cell is disclosed. Thesystem includes a reconstitution/evaporation system connected to theelectrolytic cell, a brine treatment system connected to thereconstitution/evaporation system and the electrolytic cell. A wastetreatment system is connected to the reconstitution/evaporation system.

The reconstitution/evaporation system further includes a set of effectevaporators that evaporates water vapor from the depleted brine toconcentrate the brine. Sodium chloride is precipitated from the set ofeffect evaporators to the brine treatment system. Impurities such assodium bisulfite (NaHSO₃), sodium chlorate (NaClO₃) and sodium iodide(NaI) are precipitated from the set of effect evaporators, to improvebrine quality.

The brine treatment system includes a hydrocyclone and a centrifuge thatseparates sodium chloride from water. The sodium chloride is mixed withwater to create a concentrated and purified brine. The brine is storedfor later use.

The waste treatment system includes a waste treatment tank that receiveswaste water from the set of effect evaporators. The waste water includesthe removed impurities such as sodium bisulfite (NaHSO₃), sodiumchlorate (NaClO₃) and sodium iodide (NaI). Each of the pH level and thechlorine level of the waste water is adjusted to predetermined levels.The waste water is passed through a carbon filter to complete thetreatment process.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description presented below, reference is made to theaccompanying drawings.

FIG. 1 is a general schematic drawing of a system for treating depletedbrine of a preferred embodiment.

FIG. 2 is a schematic drawing of a system for treating depleted brine ofa preferred embodiment.

FIG. 3 is a schematic drawing of a reconstitution/evaporation system ofa preferred embodiment.

FIG. 4 is a schematic drawing of a brine treatment system of a preferredembodiment.

FIG. 5 is a schematic drawing of a waste water treatment system of apreferred embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, a general schematic of system 100 for treatingdepleted brine will be described. System 100 is connected electrolyticcell 101. System 100 includes reconstitution/evaporation system 102connected to electrolytic cell 101, brine treatment system 103 connectedto reconstitution/evaporation system 102 and to electrolytic cell 101.Raw brine supply 106 is connected to brine treatment system 103. Wastetreatment system 104 is connected to reconstitution/evaporation system102 for the output of waste 105.

Referring to FIG. 2, system 200 is connected to electrolytic cell 201and forms a crystallizer which purifies depleted brine for reuse.Electrolytic cell 201 includes an anode side and a cathode sideseparated by a membrane. Each of water stream 202 and brine stream 203is connected to the anode side and flows into electrolytic cell 201. Anelectric current is supplied to electrolytic cell 201. Each of catholytestream 207 and hydrogen stream 205 is connected to and flows from thecathode side of electrolytic cell 201. Each of lean brine stream 206 andchlorine stream 204 is connected to and flows from the anode side ofelectrolytic cell 201. Lean brine stream 206 flows into brine evaporatorfeed tank 208 at a rate from approximately 2,800 gallons per minute(gpm) to approximately 3,200 gpm.

System 200 includes brine evaporator feed tank 208, which is connectedto a set of effect evaporators. Brine evaporator feed tank 208 isconnected first effect evaporator 210 with depleted brine line 209.Depleted brine line 252 is connected to depleted brine line 209 and tosalt dissolving tank 224. Lean brine line 253 is connected to lean brinestream 206 and to salt dissolving tank 224. First effect evaporator 210is connected to steam supply 211 and to cooled steam line 243. Secondeffect evaporator 212 is connected to first effect evaporator 210 withvapor line 228 and liquid line 229. Second effect evaporator 212 isfurther connected to cooled vapor line 244. Second effect evaporator 212is connected to third effect evaporator 213 with vapor line 230 andliquid line 231. Third effect evaporator 213 is connected to fourtheffect evaporator 214 with vapor line 232 and to fifth effect evaporator215 with liquid line 233. Third effect evaporator 213 is furtherconnected to cooled vapor line 245. Fourth effect evaporator 214 isfurther connected to fifth effect evaporator 215 with vapor line 234 andliquid line 235. Fourth effect evaporator is further connected toprecipitates outlet 216, cooled vapor line 247, and to waste watertreatment tank 217 with waste line 236. Waste water treatment tank 217is connected to treatment inlet 218 and to water outlet 219. Waste watertreatment tank 217 includes carbon filter 227 adjacent to water outlet219.

Third effect evaporator 213 is further connected to hydrocyclone 220with precipitate line 237. Hydrocyclone 220 is connected to waste wateroutlet 221 to waste water treatment tank 217.

In one embodiment, hydrocyclone 220 is connected to centrifuge 222 withcentrifuge line 238. In this embodiment, centrifuge 222 is connected towaste water outlet 223 to waste water treatment tank 217 and to saltdissolving tank 224 with solids line 239.

In another embodiment without the centrifuge, hydrocyclone 220 isconnected to salt dissolving tank 224.

Fifth effect evaporator 215 is further connected to salt dissolving tank224 with solids line 240, water vapor outlet 226, and to cooled vaporline 246. Salt dissolving tank 224 is further connected to raw brinetank 225 with brine line 241. Feed line 249 is connected to raw brinetank 225. Raw brine tank 225 is connected to brine treatment 251 withbrine supply line 242. Brine treatment 251 is connected to electrolyticcell 201 with brine stream 203.

In a preferred embodiment, each of first effect evaporator 210, secondeffect evaporator 212, third effect evaporator 213, fourth effectevaporator 214, and fifth effect evaporator 215 is a falling film effectevaporator. Other suitable evaporators known in the art may be employed.

In one embodiment, any of first effect evaporator 210, second effectevaporator 212, third effect evaporator 213, fourth effect evaporator214, and fifth effect evaporator 215 includes a recirculation line.

In a preferred embodiment, hydrocyclone 220 is a stainless steelhydrocyclone manufactured by ChemIndustrial Systems, Inc. of Cedarburg,Wis. Other suitable hydrocyclone separators known in the art may beemployed.

In a preferred embodiment, centrifuge 222 is a disc-stack centrifuge.Other suitable centrifuges known in the art may be employed.

In one embodiment, steam supply 211 is a multiple effect evaporator(MEE) steam driver. Any steam driver known in the art may be employed.

In another embodiment, steam supply 211 is a mechanical vaporrecompressor (MVR) power driver. Any power driver known in the art maybe employed.

In a preferred embodiment, brine treatment 251 is a clarifier to removeany sludge in the brine prior to introduction into electrolytic cell201. Other types of solids separation known in the art may be employed.

It will be appreciated by those skilled in the art that any type ofsuitable piping means may be employed to connect the previouslydescribed vessels including the effect evaporators, tanks, hydrocyclone,centrifuge, and brine treatment. It will be further appreciated that anysuitable directing devices including pumps, valves, sensors,controllers, supervisory control and data acquisition (“SCADA”) systemand software may be employed to direct steam, a liquid stream, a vaporstream and/or solids into and/or out of any of the previously describedvessels.

In other embodiments, any number of holding tanks may be connectedadjacent to any of effect evaporators 210, 212, 213, 214, and 215.

In other embodiments, any number of heat exchangers may be connected anyof effect evaporators 210, 212, 213, 214, and 215 to provide additionalheating or cooling to the effect evaporators.

Referring to FIG. 3, a preferred use of reconstitution/evaporationsystem 300 will now be described. In a preferred embodiment,approximately 45% of the depleted brine stored in brine evaporator feedtank 301 is sent to first effect evaporator 303 as depleted brinestreams 302 and 330 at a rate of approximately 2,800 gpm toapproximately 3,200 gpm. Each of depleted brine streams 302 and 330 hasa concentration level of approximately 2% NaCl and an iodine level of0.15 parts per million (ppm). Each of the concentration levels of theliquid streams as used in this application is defined as a percentage ofthe total weight. Steam 304 is introduced into first effect evaporator303 at a rate of approximately 21,000 pounds per hour (lbm/hr) to heatdepleted brine stream 302 to an operating temperature of approximately237° F. for a time of approximately 15 minutes. First effect evaporator303 has an operating pressure of approximately 7 psig. Cooled steam 325is produced by steam 304 heating depleted brine stream 302. Cooled steam325 is directed out of first effect evaporator 303 at a rate ofapproximately 21,000 lbm/hr. Water vapor 305 is evaporated from depletedbrine stream 302 in first effect evaporator 303 to create liquid stream306. Water vapor 305 is directed from first effect evaporator 303 intosecond effect evaporator 307 at a rate from approximately 20,000 lbm/hrto approximately 22,000 lbm/hr. Water vapor 305 has a temperature in arange from approximately 240° F. to approximately 245° F. Liquid stream306 is directed from first effect evaporator 303 into second effectevaporator 307 at a rate from approximately 2,800 gpm to approximately3,200 gpm. Liquid stream 306 has a concentration level of approximately12% NaCl and an iodine level of 0.22 ppm.

In a preferred embodiment, the levels and concentrations are measuredwith a spectrophotometer, such as an Agilent Cary-60 UV-Visspectrophotometer manufactured by Agilent Technologies. The iodinelevels are measured in accordance with ASTM D3869-09 (Standard TestMethods for Iodide and Bromide Ions in Brackish Water, Seawater, andBrines by the International Association for Testing and Materials (ASTMInternational)) wherein a 25 milliliter (ml) brine sample undergoesbuffering to a slightly acidic state, along with subsequent treatmentwith bromine solution, sodium formate, potassium iodide, and a starchindicator. The treated sample is then read on the spectrophotometer, ata wavelength of 570 nanometers (nm), to determine concentration.

In one embodiment, cooled steam 325 is reheated and recirculated assteam 304. Any heating and recirculating means known in the art may beemployed.

Water vapor 305 heats liquid stream 306 in second effect evaporator 307to an operating temperature of approximately 212° F. for a time ofapproximately 15 minutes. Cooled water vapor 326 is produced from watervapor 305 heating liquid stream 306. Cooled water vapor 326 is directedout of second effect evaporator 307 at a rate from approximately 20,000lbm/hr to approximately 22,000 lbm/hr. Second effect evaporator 307 hasan operating pressure of approximately 0 psig. Water vapor 309 isevaporated from liquid stream 306 in second effect evaporator 307 tocreate liquid stream 308. Water vapor 309 is directed from second effectevaporator 307 into third effect evaporator 310 at a rate fromapproximately 20,000 lbm/hr to approximately 22,000 lbm/hr. Water vapor309 has a temperature in a range from approximately 240° F. to 245° F.Liquid stream 308 is directed from second effect evaporator 307 intothird effect evaporator 310 at a rate from approximately 2,800 gpm toapproximately 3,200 gpm. Liquid stream 308 has a concentration level ofapproximately 17% NaCl.

Water vapor 309 heats liquid stream 308 in third effect evaporator 310to an operating temperature of approximately 212° F. for a time ofapproximately 15 minutes. Cooled water vapor 327 is produced from watervapor 309 heating liquid stream 308. Cooled water vapor 327 is directedout of third effect evaporator 310 at a rate from approximately 20,000lbm/hr to approximately 22,000 lbm/hr. Third effect evaporator 310 hasan operating pressure of approximately 0 psig. Water vapor 319 isevaporated from liquid stream 308 in third effect evaporator 310 tocreate liquid stream 312. Liquid stream 312 has a concentration level ofNaCl above saturation. Sodium chloride 311 is precipitated from thirdeffect evaporator 310 at a rate from approximately 8,000 lbm/hr toapproximately 9,000 lbm/hr into brine treatment system 323, as will befurther described below. The concentration level of liquid stream 312 isreduced to approximately 21% NaCl.

Water vapor 319 is directed from third effect evaporator 310 into fourtheffect evaporator 314 at a rate from approximately 20,000 lbm/hr toapproximately 22,000 lbm/hr. Water vapor 319 has a temperature in arange from approximately 240° F. to approximately 245° F. Liquid stream312 is directed from third effect evaporator 310 into fifth effectevaporator 313 at a rate from approximately 2,800 gpm to approximately3,200 gpm.

Water vapor 315 from fourth effect evaporator 314 is directed into fiftheffect evaporator 313 at a rate from approximately 20,000 lbm/hr toapproximately 22,000 lbm/hr to heat liquid stream 312 in fifth effectevaporator 313 to an operating temperature of approximately 110° F. fora time of approximately 15 minutes. Cooled water vapor 328 is producedfrom water vapor 315 heating liquid stream 312. Cooled water vapor 328is directed out of fifth effect evaporator 313 at a rate fromapproximately 20,000 lbm/hr to approximately 22,000 lbm/hr. Fifth effectevaporator 313 has an operating pressure of approximately −14 psig.Water vapor 317 is evaporated from liquid stream 312 in fifth effectevaporator 313 to create liquid stream 316. Liquid stream 316 has aconcentration level of NaCl above saturation. Sodium chloride 318 isprecipitated from fifth effect evaporator 313 at a rate fromapproximately 8,000 lbm/hr to approximately 9,000 lbm/hr into brinetreatment system 323, as will be further described below. Theconcentration level of liquid stream 316 is reduced to approximately 21%NaCl.

Water vapor 317 is directed out of fifth effect evaporator 313 at a ratefrom approximately 20,000 lbm/hr to approximately 22,000 lbm/hr. Liquidstream 316 is directed from fifth effect evaporator 313 into fourtheffect evaporator 314 at a rate from approximately 2,800 gpm toapproximately 3,200 gpm.

Water vapor 319 from third effect evaporator 310 is directed into fourtheffect evaporator 314 at a rate from approximately 20,000 lbm/hr toapproximately 22,000 lbm/hr and heats liquid stream 316 in fourth effectevaporator 314 to an operating temperature of approximately 212° F. fora time of approximately 15 minutes. Cooled water vapor 329 is producedfrom water vapor 319 heating liquid stream 316. Cooled water vapor 329is directed out of fourth effect evaporator 314 at rate fromapproximately 20,000 lbm/hr to approximately 22,000 lbm/hr. Fourtheffect evaporator 314 has an operating pressure of approximately 0 psig.Water vapor 315 is evaporated from liquid stream 316 in fourth effectevaporator 314 to form waste water 322. Waste water 322 has aconcentration level of NaCl above saturation. Sodium sulfate (NaSO₄) 320and sodium chloride 321 precipitate from waste stream 322 in fourtheffect evaporator 314 at a rate of approximately 8,000 lbm/hr. Wastewater 322 then has a concentration level of approximately 19% NaCl.Waste water 322 is directed from fourth effect evaporator 314 at a rateof approximately 3,000 gpm into waste treatment system 324, as will befurther described below.

In one embodiment, cooled water vapors 326, 327, 328, and 329 arecombined with water vapor 317 and condensed for use as a water supply.Any type of condensation means known in the art may be employed.

Referring to FIG. 4, brine treatment system 400 will now be furtherdescribed. Sodium chloride 401 is directed from third effect evaporator413 into hydrocyclone 402 at a rate from approximately 8,000 lbm/hr toapproximately 9,000 lbm/hr. Hydrocyclone 402 has a feed pressure ofapproximately 50 psi and a split ratio of 80/20, heavies (solids) tolights (liquids). Hydrocyclone 402 spins sodium chloride 401 to separatewaste water 403 from sodium chloride 404.

In one embodiment, sodium chloride 404 is directed from hydrocyclone 402into centrifuge 405 at a rate from approximately 8,000 lbm/hr toapproximately 9,000 lbm/hr. Centrifuge 405 spins sodium chloride 404 tofurther separate sodium chloride 407 from waste water 406. Centrifuge405 spins at a rate of approximately 10,000 rpm. Sodium chloride 407 isnow in a purified crystallized form.

In another embodiment, sodium chloride 404 is directed into saltdissolving tank 408 at a rate from approximately 8,000 lbm/hr toapproximately 9,000 lbm/hr.

Sodium chloride 407 is directed from centrifuge 405 into salt dissolvingtank 408 at a rate from approximately 8,000 lbm/hr to approximately9,000 lbm/hr. Sodium chloride 409 is directed from fifth effectevaporator 414 into salt dissolving tank 408 at a rate fromapproximately 8,000 lbm/hr to approximately 9,000 lbm/hr. Lean brine 416having a concentration level of approximately 2% NaCl is directed intosalt dissolving tank 408 at a rate from approximately 2,800 gpm toapproximately 3,200 gpm. Depleted brine 422 having a concentration levelof approximately 2% NaCl is directed into salt dissolving tank 408 at arate from approximately 2,800 gpm to approximately 3,200 gpm. Sodiumchloride 407 is mixed with sodium chloride 409, depleted brine 422, andlean brine 416 in salt dissolving tank 408 for a time of approximately15 minutes to form concentrated brine 410. Concentrated brine 410 has aconcentration level of approximately 21% NaCl. Concentrated brine 410 issent from salt dissolving tank 408 into raw brine tank 411 for storage.Raw brine 419 having a concentration level of approximately 21% NaCl isdirected into raw brine tank 411 at a rate from approximately 2,800 gpmto approximately 3,200 gpm. Untreated brine 420 having a concentrationlevel of approximately 21% NaCl is directed from raw brine tank 411 tobrine treatment 417 at a rate from approximately 2,800 gpm toapproximately 3,200 gpm to remove sludge. Brine supply 412 having aconcentration level of approximately 21% NaCl is directed intoelectrolytic cell 415, which is connected to reconstitution/evaporationsystem 418, at a rate from approximately 2,800 gpm to approximately3,200 gpm.

Referring to FIG. 5, waste treatment system 500 will now be furtherdescribed. Waste water 502 is directed from a fourth effect evaporatorinto waste water treatment tank 501 at a rate of approximately 3,000gpm. Waste water 502 includes sodium chlorate (NaClO₃) and sodium iodide(NaI) having concentration levels of approximately 5% and 7%,respectively. In waste water treatment tank 501, the pH level of wastewater 502 is adjusted to be in a pH range of approximately 6 to 7. Anysuitable means for adjusting the pH level known in the art may beemployed. A chlorine level of waste water 502 is measured. If thechlorine level exceeds 4 ppm, then sodium bisulfite (NaHSO₃) 503 isadded to waste water 502 to lower the chlorine level. Waste water 502 ispassed through a carbon filter to form treated water 504, which is sentto a plant outfall at a rate of 3,000 gpm.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept. It is understood, therefore, that this disclosure isnot limited to the particular embodiments herein, but it is intended tocover modifications within the spirit and scope of the presentdisclosure as defined by the appended claims.

The invention claimed is:
 1. In a system for creating a concentratedbrine from a depleted brine comprising a first evaporator, a secondevaporator connected to the first evaporator, a third evaporatorconnected to the second evaporator, a fourth evaporator connected to thethird evaporator, a fifth evaporator connected to the third evaporatorand the fourth evaporator, a hydrocyclone connected to the thirdevaporator, a centrifuge connected to the hydrocyclone, a saltdissolving tank connected to the fifth evaporator, the hydrocyclone, andthe centrifuge, a waste system connected to the fourth evaporator, amethod comprising the steps of: receiving the depleted brine in at leastone evaporator operating at a first pressure and a first temperature;receiving steam in the at least one evaporator operating at the firstpressure and the first temperature; creating a first liquid stream and afirst water vapor from the depleted brine and the steam; creating asecond liquid stream and a second water vapor from the first liquidstream and the first water vapor; creating a third liquid stream and athird water vapor from the second liquid stream and the second watervapor; removing a precipitate from the third liquid stream; separatingfirst solids from the precipitate; creating a fourth liquid stream fromthe third liquid stream and a fourth water vapor; creating a wasteliquid stream and the fourth water vapor from the fourth liquid streamand the third water vapor; removing second solids from the third liquidstream; and, creating the concentrated brine from the first solids andthe second solids.
 2. The method of claim 1, wherein the step ofcreating a first liquid stream and a first water vapor from the depletedbrine and the steam further comprises the steps of: pressurizing thefirst evaporator to approximately 7 psig; heating the depleted brinewith the steam; evaporating the first water vapor from the depletedbrine to create the first liquid stream; and, removing a cooled steamfrom the first effect evaporator.
 3. The method of claim 1, wherein thestep of creating a second liquid stream and a second water vapor fromthe first liquid stream and the first water vapor further comprises thesteps of: pressurizing the second evaporator to approximately 0 psig;heating the first liquid stream with the first water vapor; evaporatingthe second water vapor from the first liquid stream to create the secondliquid stream; and, removing a first cooled water vapor from the secondevaporator.
 4. The method of claim 1, wherein the step of creating athird liquid stream and a third water vapor from the second liquidstream and the second water vapor further comprises the steps of:pressurizing the third evaporator to approximately 0 psig; heating thesecond liquid stream with the second water vapor; evaporating the thirdwater vapor from the second liquid stream to create the third liquidstream; and, removing a second cooled water vapor from the thirdevaporator.
 5. The method of claim 1, wherein the step of creating afourth liquid stream from the third liquid stream and a fourth watervapor further comprises the steps of: pressurizing the fifth evaporatorto approximately −14 psig; heating the third liquid stream with thefourth water vapor; evaporating a fifth water vapor from the thirdliquid stream to create the fourth liquid stream; and, removing a thirdcooled water vapor from the fifth evaporator.
 6. The method of claim 1,wherein the step of creating a waste liquid stream and the fourth watervapor from the fourth liquid stream and the third water vapor furthercomprises the steps of: pressurizing the fourth evaporator toapproximately 0 psig; heating the fourth liquid stream with the thirdwater vapor; evaporating the fourth water vapor from the fourth liquidstream; precipitating a set of wastes from the fourth evaporator; and,directing the waste liquid stream to the waste system.